1. Field of the Invention
The present invention relates to a power control for a wireless telecommunication system and in particular to an apparatus for performing a power control among a mobile station, a base station apparatus and a base station control apparatus which is carried out in a mobile telecommunication system employing Wideband Code Division Multiple Access (W-CDMA).
2. Description of the Related Art
With respect to a power control method for the W-CDMA system, the 3GPP (3rd Generation Partnership Project) standard specifies as the following paragraphs (1) through (3):
(1) Open Loop Power Control (refer to the below noted non-patent document 1):
Non-Patent document 1: 3GPP TS25.331; [online], [searched on Jan. 6, 2006], Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/25-series.htm>
The Open Loop Power Control is applied to a common channel (Preamble RACH (Random Access Channel)/Preamble CPCH (Control Physical Channel)).
FIG. 1A shows an operation sequence of an initial transmission power control at a mobile station (UE) at the time of transmitting a Preamble RACH. First, a base station apparatus (Node B) performs a PCCPCH (Primary Common Control Physical Channel) transmission or a BCH (Broadcast Channel) transmission to a UE and notifies it of a cell transmission power and a pilot channel power by using a System Information Block (procedure 11).
The UE starts a call operation (procedure 12) and calculates a Path Loss with the base station of a transmission destination by subtracting a power received at the UE itself (i.e., CPICH Ec/Io or RSCP (Received Signal Code Power)) from a cell transmission power (i.e., CPICH (Common Pilot Channel) transmission power) (procedure 13). And it determines a transmission power of the UE itself with the Path Loss being considered and performs a Preamble RACH transmission by the transmission power (procedure 14).
Then a base station control apparatus (Radio Network Controller) receives a report (i.e., Measurement Results on RACH) by RACH and determines the maximum transmission power for a common channel (i.e., FACH (Forward Access Channel)) which is used when transmitting downlink control information, based on a state of the reception power of the UE.
In the case of carrying out an Open Loop Power Control, “Primary CPICH Tx power” and “Constant value” within a System Information Block are used. The Primary CPICH Tx power and Constant value are defined as shown by FIGS. 1B and 1C.
A Preamble RACH transmission power (Preamble Initial Power) transmitted from the UE is provided by the following expression (1):Preamble_Initial Power=(Primary CPICH Tx power)−(CPICH_RSCP)+(UL interference)+(Constant Value)  (1)
(2) Inner Loop Power Control (refer to the below noted non-patent documents 2 and 3):
Non-patent document 2: 3GPP TS25.211; [online], [searched on Jan. 6, 2006], Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/25-series.htm>
Non-patent document 3: 3GPP TS25.214; [online], [searched on Jan. 6, 2006], Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/25-series.htm>
The Inner Loop Power Control is a power control for an L1 line (a physical channel: DPCH (Dedicated Physical Channel), which operates independently in a DL (downlink) and a UL (uplink). It basically is operable in a single slot synchronism.
A Target SIR, that is, a target value of a Signal to Interference Ratio is retained by the Node B and UE respectively, and whose target value is basically changeable for each RAB (Radio Access Bearer) category. The target value is defined by station data at the RNC and set up at the time of a call establishment. And the Target SIR is controllable and/or updateable by a later described Outer Loop Power Control.
In the Inner Loop Power Control, an increase or decrease of a transmission power is specified by a transmission power control (TPC) bit so that an SIR comes close to the Target SIR between corresponding apparatuses (i.e., the node B and UE) A TPC bit, however, is capable of specifying only an increase or decrease. A control range, et cetera, of the TPC is specified at the time of a call establishment by using a RRC (Radio Resource Control) message.
(3) Outer Loop Power Control (refer to the below noted non-patent documents 4 and 5):
Non-patent document 4: 3GPP TS25.427; [online], [searched on Jan. 6, 2006], Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/25-series.htm>
Non-patent document 5: 3GPP TS25.433; [online], [searched on Jan. 6, 2006], Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/25-series.htm>
In the Outer Loop Power Control, a Target SIR is changed so that a line reception quality (BLER (Block Error Rate)/BER (Bit Error Rate)) comes close to a required reception quality. In this case, a control is carried out by measuring the respective line qualities of the UL and DL at the RNC and UE, respectively.
A reception quality is not always proportion ate with a reception SIR value, and the former is sometimes bad even if the latter is good. Accordingly, a line quality is measured by means of the Outer Loop Power Control and the Target SIRs are changed so as to come close to the required reception quality.
The UE observes a quality (i.e., BLER/BER) after synthesizing the maximum ratio and periodically changes Target SIRs of the Outer Loop Power Control. The change cycle is settable for each RAB.
The RNC observes a quality (i.e., CRC (Cyclic Redundancy Check)/BLER/BER) after applying a selective combined diversity process to a reception signal and periodically changes the Target SIRs of the Outer Loop Power Control. Since the control is carried out by an SRNC (Serving Radio Network Controller), it is settable in both of the frame protocol of Iur/Iub frames.
FIG. 1D shows an operation sequence of the above described Inner Loop Power Control and Outer Loop Power Control.
As a call is established among the UE, Node B and RNC (procedure 21), an individual channel signal is transmitted and received between the Node B and UE (procedure 22). The respective apparatuses of the UE and Node B measure SIRs respectively and compare the measured SIRs with the Target SIR (procedures 23 and 24).
Then, each apparatus instructs the opposite apparatus for an increase or decrease of the transmission power by using a TPC bit so that the SIR comes close to the Target SIR (procedure 25) and the opposite apparatus changes the transmission powers compliant to the instruction, followed by transmitting data (procedure 26).
The Node B calculates CRC of the data received from the UE and calculates a Transport CH BER (procedure 27), followed by reporting the obtained CRC/BER to the RNC (procedure 28).
The RNC calculates the reception quality from the received CRC by the following expression and changes the Target SIRs so that the reception quality comes close to the required reception quality (procedure 29):Reception quality=(the number of unacceptable CRC results within a predetermined period)/(the number of samples within the predetermined period)  (2)
Then it notifies the Node B of a change instruction (procedure 30).
The Node B changes the Target SIRs according to the instruction (procedure 31), and carries out an Inner Loop Power Control between the Node B and UE once again based on the changed Target SIR for changing the transmission powers (procedures 32 and 33).
The below noted patent document 1 relates to a power control between a UE and a Node B. In this system, the UE measures TFCI (Transport Format Combination Indicator) and calculates an appropriate value, thereby notifying the Node B of a TFCI field power offset and carrying out a power control.
Patent document 1: Japanese Patent Application Publication No. 2002-198903
In the conventional power control, an independent power control is carried out between the UE and Node B or between the Node B and RNC as described above. In this case, a power control is not carried out between the UE and RNC where direct telecommunication takes place, although the power is appropriately set for each section, and therefore the powers for both sections cannot be set to appropriate values simultaneously.